Many patients requiring gamma camera studies are confined to their beds. That is, the patient is so seriously ill that any movement of the patient from the bed puts the patient in jeopardy. In a great number of such cases where the patient is confined to bed, heart problems are the cause of the confinement. Accordingly, it is important to be able to acquire gamma camera images of the heart while the patient in the hospital bed with mobile and regular gamma cameras. Mobile gamma cameras are used in such cases.
Ideally the images should include single photon emission computerized tomographic (SPECT) images. To obtain good SPECT images of the heart, the camera must be able to rotate 180.degree. about the patient to acquire unhindered views of patient while going from the left posterior oblique view (LPO) to the right anterior oblique view (RAO) of the heart and surrounding environment.
FIG. 1A illustrates more precisely what is meant by LPO, RAO and left anterior oblique (LAO) and right posterior oblique (RPO) views. The tomographic view of FIG. 1A shows a cross section of the patient 13 lying on his back on hospital bed 14. The heart 10 is shown on the left side of the tomographic image which means that the patient's feet are going into the paper and the patient's head is toward the viewer. The patient's torso is shown traversed by eight axes and directions which define the related views. The eight axes are the anterior axis 2, the right anterior oblique axis 3, the right axis 4, the right posterior oblique axis 5, the posterior axis 6, the left posterior oblique axis 7, the left axis 8 and the left posterior oblique axis 9. To acquire a tomographic image of the heart the detector head should rotate through the 180 degrees while it is as close as possible to the heart; i.e. from the LPO view to the RAO view.
FIG. 1A shows that when the patient is lying on his back, bed 14 interferes with the gamma rays during at least a portion of the scan.
The views illustrated in FIG. 1A should be acquired when the patient is lying so that no part of the range of patient observation by the camera is obstructed by the bed. It is desirable that the detector head to be as close as possible to the patient's heart during the acquisition of the views.
Cardiac SPECT is usually accomplished with 180.degree. rotation of the camera detector about the patient. Angular rotations larger than 180.degree. are also used. Modern reconstruction techniques enable rotations less than 180.degree. to be used. Accordingly, whenever 180.degree. rotation is referred herein more and less than 180.degree. are also included.
Present day mobile gamma camera arrangements do not perform SPECT imaging because when the patient is on his back the view of the patient's heart when rotating from LPO to RAO is obstructed by the bed. Present day gamma camera arrangements, for SPECT, include an elongated, low gamma ray absorbence, patient support or bed. Thus, to be used the patient has to be moved from the regular hospital bed to the low gamma ray absorbence support of the camera arrangement.
The requirement to move the patient is also a serious detriment. The patient must be moved when using present day gamma cameras for SPECT imaging; since, it has not been possible to acquire the necessary views for a proper medical diagnosis if the patient remains in the hospital bed because of the interference of the regular hospital bed with the emitted gamma rays. The interference of the regular hospital bed with the acquisition of such images made it necessary in the past for the patient to be transferred to the imaging device that included a bed or support of low gamma ray absorbence.
Presently there are no known mobile gamma camera arrangements that can acquire satisfactory SPECT images of the bedridden patient's heart.